1. FIELD OF THE INVENTION
The present invention relates to a center mechanism of a tire press for inflating a bladder into close contact with the inner peripheral surface of a green tire.
2. DESCRIPTION OF THE RELATED ART
Generally, before a green tire is molded by a space formed by clamping of an upper mold (upper metal mold) and a lower mold (lower metal mold) of a tire press, shaping for inflating a bladder into close contact with the inner peripheral surface of a green tire is applied by a center mechanism.
As shown in FIG. 3, the conventional center mechanism is arranged in the center of a lower mold 52 on a base frame 51, and a well 54 capable of receiving a bladder 53 therein is moved up and down with respect to the lower mold 52. A lower bead ring 57 supporting a lower bead 56 of a green tire 55 is mounted on the side end of the lower mold 52 of the well 54, and is moved up and down by a vertically movable cylinder 58 provided on the lower side of the base frame 51. The bladder 53 is receivably arranged in the well 54, and the upper and lower ends of the bladder 53 are clamped by an upper clamp portion 59 and a lower clamp portion 60. In the center of the upper clamp portion 59 is supported a center post 61 which passes through the bladder 53 and further extends through the lower clamp portion 60 and the well 54. The center post 61 is moved up and down by an elevating cylinder 62 to expand and contract the bladder 53. The lower clamp portion 60 is supported on the elevating cylinder 62 by a tubular member 63 fitted in the outer periphery of the center post 61, and is moved up and down by an elevating cylinder 64 provided on the lower side of the well 54.
In the center mechanism constructed as described above, the well 54 is moved up to tear off the vulcanized tire 65 from the lower mold 52. However, when a tire having a large compression is vulcanized, an on-allowance of the lower bead 56 relative to the lower bead ring 57 is so lessened that when the tire is torn off from the lower mold 52, the bead is possibly disconnected from the ring. This makes difficult to hold the inner periphery of the vulcanized tire by a delivery loader (unloader), resulting in the inferior removal.
In order to cope with the flat tire as mentioned above, there has been known a center mechanism in which a lower bead ring for supporting a lower bead of a green tire is secured to a lower mold. In the center mechanism of this kind, the vulcanized tire is held by the unloader and torn off from the lower mold, which can fully correspond to the flat tire also.
However, in the type of securing the lower bead ring among the center to the lower mold, when the lower mold is replaced with one different in size, the lower bead ring is to be deviated from the lower clamp portion by a height of the lower mold, thus making it necessary to set the lower clamp portion so as to be parallel with the lower bead ring. By doing so, when a deviation in height occurs, the bladder cannot be inflated into close contact with the inner peripheral surface of the green tire, failing to apply the shaping to the green tire. For this reason, the lower bead ring is moved up and down by the elevating cylinder for adjustment thereof, but the position of the lower clamp ring portion cannot be adjusted with good accuracy depending on the elevating cylinder.
It is an object of the present invention to provide a center mechanism capable of changing a lower clamp portion to a height position of a lower metal mold (a position parallel with a lower bead ring) irrespective of the size of the lower metal mold.
The present invention provides a center mechanism of a tire press, in which an upper clamp portion and a lower clamp portion freely inserted into the inner surface of a green tire inserted into closing upper and lower metal molds are separately moved up and down, comprising a well for receiving a bladder, a lower bead ring for supporting a lower bead of a green tire being secured to said lower metal mold, said center mechanism comprising: a center post for supporting the upper clamp portion, a hollow member for supporting the lower clamp portion and extending around the center post, a support member provided below the hollow member, a first vertically moving member connected to the lower end of the center post and mounted on the support member, a tubular member positioned downward of the support member and positioned around the first vertically moving means and provided with an external thread portion, an elevating member for rotatably holding an internal thread portion engaged with the external thread portion, and driven and rotated, and a second vertically moving means mounted on a frame connected to the elevating member to support the lower metal mold.
In this case, if the size of the lower metal mold is changed, the internal thread portion engaged with the external thread portion is rotated and driven whereby the lower clamp portion can be moved to the position adjusted to the height of the lower metal mold, making it possible to automatically cope with the change of the height of the lower metal mold. Since the hollow member and so on are arranged around the center post, the whole center mechanism can be received compactly.
Preferably, a disengageable stopper member for stopping the downward movement of the lower clamp portion is provided between said elevating member and said frame.
In this case, it is possible to prevent the lower clamp from being forced down by fluid pressure exerting on the bladder in shaping of the green tire. Therefore, no change occurs in a positional relation between the lower clamp portion and the lower bead ring.
Further, preferably, as the first vertically moving means, a fluid pressure cylinder capable of being moved up and down to a changeable fixed position is used.
In this case, the vertical movement of the first vertically moving means is controlled whereby the fixed position of the upper clamp portion can be automatically changed according to the change of the size of the lower metal mold.
The second vertically moving means has a first position for making the lower clamp portion parallel with the bead ring, a second position for making it position above the bead ring, and a third position which moves down in order to receive the bladder in the well, the lower clamp portion being designed to hold and clamp the lower end of the bladder between the inner lower ring and the outer lower clamp ring, preferably, being provided with a third vertically moving means for vertically moving the lower clamp ring.
In this case, the lower clamp portion is moved from the first position to the second position by the second vertically moving means, after which the lower clamp ring is moved down by the third vertically moving means, whereby the clamp of the lower end of the bladder can be released. Since the lower clamp ring is moved up and down with respect to the lower ring by the third vertically moving means, operating properties in exchange of the lower portion of the bladder at the lower clamp portion are excellent.